Worm Gear

A worm gear is a type of staggered shaft gear that transmits motion between two shafts that are not intersecting or parallel. The worm gear is threaded into a round bar and a worm wheel is the gear that meshes with the worm at a 90-degree angle.  A set of the worm and worm wheel together is called a worm gear. The worm is the driver, and the worm wheel is the driven shaft.  [21]

There are three types of worm gears: cylindrical worm gear, drum-shaped worm gear and throated worm gear.

To reduce wear from the constant mesh between the worm and worm wheel, the worm is typically made of a harder material. 

Applications include speed reducers, elevators, machine tools, chain blocks, fishing reels and automotive power steering.